From the Buddha to modern gurus of self-help, there have been more than 100 exercises proposed which are alleged to increase lasting happiness, says Professor Martin Seligman a contributor to BBC Two's The Happiness Formula.

In strange contrast, scientific investigation until recently thought none of these exercises would, as there was an unchangeable and biological "set point" for happiness.

This suggested that our levels of happiness were largely pre-determined by our genes and our upbringing, varying slightly but always returning to our set point of happiness.

It also explained the annoying fact that lottery winners eventually revert to their customarily curmudgeonliness and the rosier finding that paraplegics eventually return to almost the same happiness level they enjoyed before their accident.

I have spent more than 20 years testing the effects of various psychotherapies and drugs on depression.

So when I became a positive psychologist, I first explored many of these exercises and then decided to test rigorously whether any of them really increased happiness.

I began by teaching positive psychology to undergraduates: each week I assigned an exercise along with more traditional readings.

I do not think I ever heard the word "life-changing" more often in my 40 years of teaching.

Positive feedback

Then I started teaching a six month telephone course to 1,000 coaches, clinical psychologists, parents, and educators.

Professor Seligman advocates exercises to improve well-being

Each week I would assign one exercise and the students would give it to their clients and carry it out themselves.

So I was ready to try the gold standard: random assignment, placebo controlled tests of each exercise, looking for lasting changes in well-being.

We told people that we wanted to find out which interventions work to raise happiness and which are bogus.

About 500 people soon volunteered and each person received a battery of tests, one simple week-long web exercise (no human hands) and then was tested about their well-being repeatedly for the next six months.

Three exercises proved to be placebos and three worked well, producing lasting reductions in depression and lasting increases in happiness.

The three that worked were "three blessings" - writing down three things that went well today and why; "the gratitude visit" - writing a gratitude testimonial and delivering it personally; and "using your signature strength in a new way" - taking the signature strength test and using your highest strength in a new way.

You can find out more about these exercises by following the link on the right.

Decreasing depression

We continue to test new exercises in this way, hoping to separate the wheat from the chaff.

We looked at the effect on severe depression of doing just the first web exercise, three blessings.

Overall then there is good evidence that several simple exercises increase happiness and decrease depression.

The set point theory of well-being appears to be wrong.

While these exercises increase well being among relatively untroubled people, there is one surprising implication for serious depression: psychotherapy traditionally is where you go to talk about your troubles.

The psychotherapy of the future may also be where you go to talk about positive emotion, your strengths and virtues, and how to build more meaning into your life.

You can watch The Happiness Formula on BBC Two on Wednesdays at 1900 BST